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TEST CIRCUIT FOR MULTIPLE SWITCH BOARDS.

No. 888,495. Patented May 29, 1888.

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O. E. SORIBNER.

' TEST CIRCUIT FOR MULTIPLE SWITCH BOARDS. No. 383,496. Patented May 29, 1888..

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CHARLES E. SCRIBNER, OF CHICAGO, ILLINOIS, ASSIGNOR TO THE \VESTERN ELECTRIC COMPANY, OF SAME PLACE.

TEST-CIRCUIT FOR MULTIPLE SWBTCH BOARS.

$PECIFICATION forming part of Letters Patent No. 383,4:95, dated May 29, 1888.

Application filed December 27, 1886. Renewed November 21, 1887. Serial No. 255,769. (Nb model.)

To aZZ whom it may concern:

Be it known that I, CHARLES E. SORIBNER, a citizen of the United States, residing at Ohicago, in the county of Cook and State of Illinois, have invented a certain new and useful Improvement in Test Circuits for Multiple Switch-Boards, (Case 118,) of which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawings, forming a part of this specification.

My invention relates to multipleswitchboard systems of telephone-exchange in which the different subscribers are provided with metallic circuits each connected with a different spring-jack switch upon the different switchboards.

The object of my invention is to enable the operators at the different boards to test to determine whether any line is busy when said lines are connected with ordinary spring-jack switches, and without the use of special testwires and special connections therefor.

My invention herein is an improvement upon the system described and claimed in my patent, No. 305,021, of September 9, 1884.

The spring-jack which I use herein requires only the same number of points or connections as that described in my said patent. I use, however, a pair of loop-plugs with doublestranded cords and key-board apparatus of novel construction. The key-board apparatus I will only describe incidentally herein, as the improvements therein form the subjectmatter of another application, and as it is evident that other key-board apparatus which is well known might be used in connection with the circuits which form the subjectmatter of my invention claimed herein.

Myinvention consists in connecting the different telephone-lines through the switches upon the different boards and back to the subscribers stations, respectively, and in connecting the different lines at their respective stations in such manner that one branch will be open at the subscribers station when the telephone is in its normal position upon the switch-lever, while the branch containing the bell and generator will be closed to ground.

From the line side of the open branch containing the telephone I provide means for closing said branch to ground when it is desired to call the central office. By this arrangement of circuits of the telephouelines it is evident that when the circuit of a battery including a 5 5 telephone is closed to the test-piece of one of the switches at either of the switch-boards the circuit will be completed through the branch of the line connected with the frames of the switches to the subscribers switch, and thence through the branch containing the subscribers bell and generator to ground. Thus when a test is made the operator will know by the click in his telephone that the line tested is free. When, however, a line is connected with another in metallic circuit and the pair of loopplugs are inserted, respectively, in switches of the different lines for connecting said lines together, the springs of the said switches will be lifted from their contactpoints and connected with the tips of the two plugs. The springs are thus connected to gether through the strand of the cord which connects the tips, while the frames of the jacks are connected together through the mediu n1 of the sleeves of the plugs and the strands connecting said sleeves together. Under such conditions, as is well known, an operator test ing the line will get no circuit through his telephone and hear no click, and hence Will know that the line is busy.

My invention is illustrated in the accompanying drawings, in which Figure 1 is a diagram illustrative of two metallic circuits connected with their spring-jack switches on two multiple switch-boards and key -board apparatus at one of said switchboards. Fig. 2 is a diagram of the circuits at the subscribers station. Fig. 3 is a sectional detailed View of one of the loop-plugs provided witha metallic heel connected with the tip.

Like parts are indicated by similar letters of reference throughout the different figures.

As shown in Fig. 2, I provide a branch, a, in which is included a key, I). By means of 5 this key the branch 0 of any line which connects through the different switches of the line may be closed to ground while the subscriber is sending in a call. The circuit thus formed may be traced,beginning at the grou ndline d at the subscribers station, through the subscribers generator and bell, to the subscribers telephone switch lever e, thence through branch 0 of the circuit of the line, through the contact-points of the switches fg, to the subscribers individual annunciator h, and thence by branch 1' of the line to branch at at the subscriber s station, and thence to key b, which is depressed when the subscriber rings. Thus the circuit is completed from the subscribers station to the central office and back again to ground at the subscribers station.

Branch z of the telephone-line,it will be seen, is connected with the insulated frames of the different switches, and when the telephone at the subscribers station is hung upon the switch, as shown, said branch '5 remains open at the subscribers station. We have then a metallic circuit consisting of two branches, 0 and 2'. Branch 1' is open at the subscribers station as long as the telephone 70 remains upon the switchlever. On the other hand, branch 0 is closed to ground when the telephone is is upon the switch-lever. Thus, tracing from the frames of the switches fg by line t, it will be found that there will be no connection from line 1' to ground as long as the telephone 70 remains upon the switch at the subscribersstation. Tracing, however, from the frame of any switch f or g at the central office by wire Z to the spring of the switch on the last board, and thence to branch 0, and thence to the sub scriber s station, and through the bell and generator to ground d, it will be found that all the frames or test-pieces of the switches of the line are normally connected to ground at the subscribers station by branch 0. Thus, when a test is made at any spring-jackf or g of a line, circuit may be found to ground from branch 0 to the subscribers station. If, how ever, a plug is inserted in any spring-jack f or g of the line, all the frames of the switches of the line will be disconnected from said branch 0 of the line at the switch where the plug is inserted. Thus when a plug is inserted in any switch of the line, and a test is made at any other board, no circuit will be found, and the operator will know that the line is busy.

Upon inserting a plug at any spring-jack of the line the connection between the test-frames and the branch 0 of the line will be opened at the spring-jack where the plug is inserted, and as branch 2' is normally open at the subscribers station a test at any spring-jack will indicate an open circuit, and consequently that the line tested is in use at some other board, as before described.

I have described a key, I), at the subscribers station as operated by hand. It is evident that this circuit may be closed automatically by turning the crank of the generator in the same way, for example, that the shunt around the generator is now usually opened.

There are many different devices for doingthis work, which are well known in the art, by means of which the push-button b, operated by hand, might be dispensed with.

Having thus described my invention,I claim as new and desire to secure by Letters Patent- 1. In a multiple-switchboard system of telephone exchange, the combination, with a spring-jack switch on each of the boards, of a circuit extending from ground at the subscribers station through his generator and bell and switch to the central office, through said switches and an annunciator to a line connected with the test plates or frames of said switches and extending to the subscribers station, and two branches of said line at the sub scribers station, one branch including the telephone and being normally open at the telephone-switch, and the other branch being connected with a normally-open ground-switch, whereby signals may be sent between the subscribers station and the central office, substantially as described.

2. In a multiple-switchboard system, the combination of switches, one on each board for each telephone-line of the telephone-lines connected therewith, each line consisting of two branches, one branch of which, after passing through its switches and an annunciator, being connected with the other branch, which other branch is connected with the insulated frames or contact-pieces of the switches of the line, said branches extending to the subscribers station, and the former being connected with the subscribers.telephone-switch, and when the telephone is on the switch through the bell and generator to ground, and the other branch, which includes the telephone, being normally open at the subscribers telephoneswitch when the telephone is hung thereon, and a branch connection including a groundswitch on the line side of the telephone, whereby a complete circuit may be formed from ground at the subscribers station through the switches and the annunciator of the line at the central office, and back to ground at the subscribers station, substantially as and for the purpose specified.

3. In a multiple-sWitch-board system of telephoneexchange, switches f g on different boards and telephone-line consisting of branches 07:, connected therewith, and through an annunciator, h, said branches extending to the subscribers station, and branch 0 being normally connected with ground, and branch 6 being normally open, in combination with a loop-plug inserted in switch f at the central office, whereby the insulated frames of the switches are disconnected from branch 0, substantially as shown and described.

4:. A subscribers circuit extending from ground at the subscribers station through the springs of a series of switches on different sec tions of a multipleswitch-board and an annunciator back through the insulated frames or test-pieces of said switches, and thence back IlO to the subscribers station, the portion of the In witness whereof I hereunto subscribe my circuit connecting with the frames or test name this 16th day of November, A. D. 1886. pieces being normally open at said subscrib- 1 I 1 ers station, in combination Witha plug which, CHABLES SORI'BNER 5 being inserted in a switch at either of the Witnesses:

boards, opens the metallic circuit at said GEORGE P. BARTON,

switch. WM. M. GILLER. 

